"[It's] a noble concept, but one that will cost many billions of dollars, and we do not have a viable pathway to that at this point," de Blasio said.

A City Hall spokeswoman downplayed the differences between the married couple, saying they agree it's a "noble" goal but "the Mayor also made clear many significant challenges must be addressed before that can be achieved."

In the interview, McCray also hinted that the pair's two politically active, college aged kids might be backing U.S. Sen. Bernie Sanders over Hillary Clinton in the Democratic primary.